Sea Level Rise Impact on Drainage Network Properties following Restoration Activities

Abstract:

For centuries estuarine systems have been losing portions of their natural domain as a consequence of human actions. In the past, estuaries were perceived as sources of disease, often drained or heavily engineered. Our current understanding shows that estuaries are instead rich ecosystems that need to be restored to their natural state. However, returning these areas into the tidal system may cause morphological changes on its present behavior. For this reason, it is important to understand, and attempt to predict, what morphodynamic changes an estuarine system may experience due to different restoration actions.

In order to drain and use portions of the estuary, dikes are often built to disconnect them from the estuary. In this work we focus our attention on the restoration of these areas and specifically on dike removal. Dikes may be totally or partially removed to allow the tidal flow to enter into the area being restored. Morphodynamic effects of dike removal are computed numerically using Delft3d. Different dike removal configurations are studied and their effect on the recovery of the estuary quantified computing the probability distribution of drainage area and drainage volume. Tidal network characterization is carried out using a new approach that considers spatial hydrodynamic fields during a complete tidal cycle. Connectivity is thus allowed to evolve with time. The impact of different restorations strategies in the drainage area and volume of the network has been studied in the short term (5 -10 years) and in the long term (100 years).

Results show the differences in tidal network characteristics after different dike removal actions for different scenarios. These differences are quantified with the new approach, allowing to highlight the changes that induce deep behavioral change in the system. The importance of sea level rise in these behavioral changes is also assessed in the study.